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Warmer spring temperatures compounding pine beetle epidemic

March 14, 2012

March 14, 2012 Jeffry Mitton/Scott Ferrenberg

Because of decades of warmer springtime temperatures, mountain pine beetles are now maturing sooner and flying earlier, according to a CU-Boulder study led by ecology and evolutionary biologist Jeffery Mitton.

The result, says Mitton, is instead of producing only one generation of tree-killing offspring annually, some populations of pine beetles are now reproducing two generations per year.

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Warmer spring temperatures compounding pine beetle epidemic

March 14, 2012 Jeffry Mitton/Scott Ferrenberg

Because of decades of warmer springtime temperatures, mountain pine beetles are now maturing sooner and flying earlier, according to a CU-Boulder study led by ecology and evolutionary biologist Jeffery Mitton.

CUT 1 “So they’re coming out fully a month earlier, maybe more than 6 weeks earlier than the historic main pulse. (:08) It used to be the case that a single female would put out approximately 60 eggs. If all of those eggs survived and emerged as adults then she would have 60 offspring in one year. “ (:22)

The result, says Mitton, is instead of producing only one generation of tree-killing offspring annually, some populations of pine beetles are now reproducing two generations per year.

CUT 2 “Now a female can have 60 offspring from June to August. And each one of those would have 60 offspring to give her, in one-year, 60 offspring plus 3,600 grandchildren. (:14) So what that means is there has been an exponential increase in the number of bark beetles (available in the forest or) flying in the forest and very simply, the more beetles that fly, the more trees are attacked.” (:28)

And, Mitton says, for the first time these effects are being felt at higher elevations. The warmer temperatures are allowing beetles to attack trees that at one time were protected by colder temperatures.

The study site at CU’s Mountain Research Station just west of Boulder is at 10,000 feet, 1,000 feet higher than where the beetles have historically thrived.

CUT 3 “Count the temperature degree days between January and the end of June over the last 40 years, that number has increased by 58 percent at the site where we study. (13) So it has been an enormous change in early spring temperatures. Spring times are warmer there and anyone who skis or is out and about knows that the snow is melting out earlier now than it used to.” (:28)

Mitton’s assistant and co-author of the study, Scott Ferrenberg, adds that the problem is compounded by the fact that the higher elevation pine trees are not prepared to fend off attacks from the mountain pine beetle.

CUT 4 “Because those trees have experienced a lesser history of being attacked, there has been less selective pressure of them to defend themselves against bark beetles. (:07) And we’re finding that as beetles move to higher and higher elevations the trees are easier for them to kill. And so it magnifies the effect of this epidemic. (:17)

The two scientists have been documenting the life cycle and activities of the mountain pine beetle at the research station since 2009.

The mountain pine beetle is the most destructive western forest insect. Normally, it plays an important role in the life of a forest, attacking and killing old or weakened trees to make way for a younger, stronger forest.

But this epidemic is the most destructive in history, encompassing an area from northern New Mexico to the Yukon Territory near Alaska.